Add HttpUrlConnection backed implementation of CronetEngine.

components/cronet/android/api/src/org/chromium/net/JavaCronetEngine.java

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.net;
+
+import static android.os.Process.THREAD_PRIORITY_BACKGROUND;
+import static android.os.Process.THREAD_PRIORITY_MORE_FAVORABLE;
+
+import java.io.IOException;
+import java.net.Proxy;
+import java.net.URL;
+import java.net.URLConnection;
+import java.net.URLStreamHandler;
+import java.net.URLStreamHandlerFactory;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.Executor;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ThreadFactory;
+
+/**
+ * {@link java.net.HttpURLConnection} backed CronetEngine.
+ */
+final class JavaCronetEngine extends CronetEngine {
+    private final String mUserAgent;
+
+    private final ExecutorService mExecutorService =
+            Executors.newCachedThreadPool(new ThreadFactory() {
+                @Override
+                public Thread newThread(final Runnable r) {
+                    return Executors.defaultThreadFactory().newThread(new Runnable() {
+                        @Override
+                        public void run() {
+                            Thread.currentThread().setName("JavaCronetEngine");
+                            android.os.Process.setThreadPriority(
+                                    THREAD_PRIORITY_BACKGROUND + THREAD_PRIORITY_MORE_FAVORABLE);

[pauljensen, 2015/12/08 19:49:52]

why one above background?  I think Cronet's network thread is just background.

[Charles, 2015/12/11 16:45:39]

Added comment explaining priority selection.

+                            r.run();
+                        }
+                    });
+                }
+            });
+
+    JavaCronetEngine(String userAgent) {
+        this.mUserAgent = userAgent;
+    }
+
+    @Override
+    public UrlRequest createRequest(String url, UrlRequest.Callback callback, Executor executor) {
+        return new JavaUrlRequest(callback, mExecutorService, executor, url, mUserAgent);
+    }
+
+    @Override
+    public UrlRequest createRequest(
+            String url, UrlRequest.Callback callback, Executor executor, int priority) {

[pauljensen, 2015/12/08 19:49:52]

I see you're ignoring priority.  That's probably fine, but perhaps we should
document the limitations of this implementation (like ignoring priority, netlog,
no bidiStream, no cache, no NQE etc) on line 25.

[Charles, 2015/12/11 16:45:39]

Done.

+        return new JavaUrlRequest(callback, mExecutorService, executor, url, mUserAgent);
+    }
+
+    @Override
+    BidirectionalStream createBidirectionalStream(String url, BidirectionalStream.Callback callback,
+            Executor executor, String httpMethod, List<Map.Entry<String, String>> requestHeaders) {
+        throw new UnsupportedOperationException(
+                "Can't create a bidi stream - httpurlconnection doesn't have those APIs");
+    }
+
+    @Override
+    boolean isEnabled() {
+        return true;
+    }
+
+    @Override
+    public String getVersionString() {
+        return "HttpUrlConnection";

[pauljensen, 2015/12/08 19:49:52]

This should really include a version string so we know what version we're
dealing with in bug reports.
How about: "CronetHttpURLConnection/" + Version.getVersion();

[Charles, 2015/12/11 16:45:39]

Done.

+    }
+
+    @Override
+    public void shutdown() {
+        mExecutorService.shutdown();
+    }
+
+    @Override
+    public void startNetLogToFile(String fileName, boolean logAll) {}
+
+    @Override
+    public void stopNetLog() {}
+
+    @Override
+    public byte[] getGlobalMetricsDeltas() {
+        return new byte[0];
+    }
+
+    @Override
+    public void enableNetworkQualityEstimator(Executor executor) {}
+
+    @Override
+    void enableNetworkQualityEstimatorForTesting(
+            boolean useLocalHostRequests, boolean useSmallerResponses, Executor executor) {}
+
+    @Override
+    public void addRttListener(NetworkQualityRttListener listener) {}
+
+    @Override
+    public void removeRttListener(NetworkQualityRttListener listener) {}
+
+    @Override
+    public void addThroughputListener(NetworkQualityThroughputListener listener) {}
+
+    @Override
+    public void removeThroughputListener(NetworkQualityThroughputListener listener) {}
+
+    @Override
+    public URLConnection openConnection(URL url) throws IOException {
+        return url.openConnection();
+    }
+
+    @Override
+    public URLConnection openConnection(URL url, Proxy proxy) throws IOException {
+        return url.openConnection(proxy);
+    }
+
+    @Override
+    public URLStreamHandlerFactory createURLStreamHandlerFactory() {
+        return new URLStreamHandlerFactory() {
+            @Override
+            public URLStreamHandler createURLStreamHandler(String protocol) {
+                return null;

[pauljensen, 2015/12/08 19:49:52]

perhaps instead of returning null, return:
new URLStreamHandler() {
    @Override
    URLConnection openConnection(URL u) throws IOException {
        return u.openConnection();
    }
    @Override
    URLConnection openConnection(URL u, Proxy proxy) throws IOException {
        return u.openConnection(proxy);
    }
}

[Charles, 2015/12/11 16:45:39]

That causes infinite recursion. Added a comment.

+            }
+        };
+    }
+}